Abstract
Movement of labeled amino acids from leaf blades to sheaths was followed after supplying 13NH3 gas, 14CO2, or 14C-amino-acids to attached blades of barley plants.
Blades of turgid and wilted plants fed 13NH3 (at about 120 to 700 microliters per liter) had incorporated 13N mainly into free glutamine and glutamate after 30 minutes, and turgid blades had exported 1 to 3% of the assimilated 13N to the sheaths, mostly as glutamine and glutamate. Wilted blades exported less of the assimilated 13N than turgid blades even though they exported 14CO2 assimilates as actively as turgid blades.
When substrate amounts (about 0.28 micromole) of [14C]glutamate and [14C]proline were applied to turgid and wilted blades, these amino acids entered the phloem and were translocated at velocities similar to those for 14CO2 assimilates (about 0.2 centimeter per minute). Wilted blades metabolized tracer amounts of [14C]glutamate to glutamine and proline, and exported 14C in the form of these three amino acids. Approximate calculations of mass transfer rates of glutamate, glutamine, and proline made for wilted blades indicated that glutamine and glutamate together carried 76 micrograms of N per day, whereas proline carried only about 9 micrograms of N per day.
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Selected References
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